1. Field of the Invention
The invention relates to a fan wheel for conveying an air mass, especially for a turbo charger, ventilator or a similar device, comprised of a base body with a central axis of rotation, wherein the base body is comprised of two cover discs positioned approximately congruently opposite one another, between whose inner end faces facing one another fan blades are arranged which are formed as monolithic parts at least on one of the cover discs and have an axial contact surface against which an oppositely positioned axial contact surface of the other cover disc rests, and with fastening means in the area of the contact surfaces for non-detachably connecting the cover discs to one another.
2. Description of the Related Art
Such a known fan wheel is disclosed in DE 85 18 403. It is comprised of two cover discs approximately parallel to one another between which the fan blades are arranged. At one of the cover discs grooves are formed which rest against the other cover disc and thus form the fan blades. For connecting the cover discs, they are glued, welded or connected by separate rivets to one another in the area of the contact surfaces. The thus constructed fan wheels must be balanced before being operated because unbalance will usually occur due to tolerances, material concentrations etc. and must be equalized because of the high operational rpm of the turbo charger of, for example, 20,000 rpm. The manufacture of such fan wheels therefore requires many parts, is labor-intensive, and expensive.
The invention has the object to develop a fan wheel of the aforementioned kind such that it can be produced in a few simple manufacturing steps and can be assembled to a ready-to-use state without requiring balancing.
This object is solved according to the invention in that the cover discs are comprised of a material that can be embossed and in that the fan blades are embossed axially out of the material of a cover disc, wherein the edge between the plane of the cover disc and the sidewall of a fan blade positioned substantially at a right angle to the plane of the cover disc as well as the edge between the sidewall and the contact surface are rounded with a radius of approximately 0.5 to 2 mm.
The use of a material that can be embossed such as, for example, sheet metal that can be deep-drawn, i.e., sheet steel, stainless sheet steel, sheet aluminum etc., allows to emboss during the manufacture of the cover discs simultaneously the fan blades over a portion of or over their entire axial height. With this non-cutting forming and embossing, the material quantity is not changed so that a final balancing is no longer needed. Due to the monolithic embodiment of the fan blades with the cover disc, only a few fastening points are required. The fan wheel is comprised of only two axially joined parts wherein one axial contact surface of one of the cover discs rests fixedly against the axial contact surface of the other cover disc. All edges that are exposed to the airflow are rounded so that a high conveying efficiency is provided with minimal noise development.
Expediently, the cover discs are connected positive-lockingly to one another in the area of the contact surfaces. Advantageously, connecting locations are provided only in the area of the contact surfaces.
In an advantageous embodiment of the invention, fixation openings can be provided at one of the contact surfaces of one cover disc. Fixation noses, for example, by drawing or impact extrusion, are formed at the oppositely positioned contact surface of the second cover disc. When aligning the cover discs relative to one another, the fixation noses engage the oppositely positioned fixation openings which are advantageously provided with a countersunk portion at the rivet head side so that the position-exact correlation of the two parts is ensured. Since the fixation noses and fixation openings are provided exclusively on the contact surfaces of the fan blades, the correct rotational position of the cover discs relative to one another is determined at the same time so that all fan blades, uniformly distributed in the circumferential direction of one cover disc, contact the correlated contact surfaces of the other cover disc. Expediently, the fixation noses are formed by impact extrusion resulting in rivet bolts with which the cover discs are connected to one another in a non-detachable manner in the area of the contact surfaces. Since with this connecting technique no material is added, the otherwise required balancing measures are no longer needed.
Expediently, the fan blades are formed by the walls of an embossed depression, wherein the depression at the same time provides strengthening of the cover disc.
The depressions are advantageously closed off at their ends and extend in the radial direction only over a portion of the radius of the cover disc. The radial ends of the depressions, i.e., of the fan blades, have a rounded end face.
Advantageously, one cover disc is provided, especially at the inner side facing the airflow, with a waffle-like or scale-like embossment. This can provide an improved flow of the airflow conveyed by the fan wheel. The waffle-like embossment moreover avoids stress in the cover disc so that a planar, distortion-free shape of the cover disc is ensured. Even at high rpm no unbalance will be observed. The scale-like embossment also eliminates the need for a planing action of the cover disc subsequent to embossing the depressions, which form the fan blades, and, moreover, can provide flow-technological advantages and can dissipate heat that develops.